1. Field of the Invention
The present invention relates to a processing controller, a data communication apparatus such as a personal computer, and a program for the controller and apparatus. Particularly, the invention relates to a processing controller, a data communication apparatus that incorporates a software modem to stabilize a connection of a communication line between data communication apparatuses, and a program for the controller and apparatus.
2. Description of the Related Art
In order to maintain a stable operation of a communication line while the communication line is being connected to a bulletin board system (BBS) or other data communication apparatus, telecommunication equipment such as a modem always monitors line quality, and automatically resets communication functions and performance such as a communication speed and a modulation system (i.e., retraining, and rate renegotiation). With the increase in the operating speed of CPUs in recent years, software is being developed for telecommunication equipment such as modems. The bulletin board system conventionally refers to the whole of personal computer communication services, and nowadays refers to a data communication apparatus provided in a Web site mode on the Internet. The retraining refers to a negotiation operation that two sets of telecommunication equipment (i.e., modem) carry out to determine the setting of communication functions and performance by mutually exchanging information about communication speed, modulation system, error correction function, and data compression procedure, to establish communications. Particularly, negotiation to reset a communication speed is called rate renegotiation. The retraining is the processing to renegotiate communication functions and performance currently in use, without re-connecting the mutually-connected two modems. The retraining occurs when a line state changes as a result of increase in the amount of static electricity on the line, for example. Usually, this processing takes a few seconds.
Patent literature 1 discloses an information processor that restricts power consumption of a CPU by variably controlling the clock frequency of the CPU using a software modem, that is, a software system for a computer main body to execute a part of the functions of a modem that connects between the computer and an analog communication line. The patent literature 1 also discloses an information processor that restricts communication errors such as a connection refusal and a timeout, by variably controlling the clock frequency following a necessary CPU load that changes according to a negotiation state.
Patent literature 2 discloses a software modem for a data communication apparatus, in which, when there is an instruction to process a specific application with a higher processing priority than that of a modem processing of resetting communication functions and performance, the software modem starts processing this specific application even when the modem processing is being carried out. In order to properly execute the modem processing while properly executing the processing of other applications, the software modem changes a communication speed according to the number of applications being started, the state of the load of the applications being started on the CPU, and the time required for the modem processing.
Patent literature 1: Japanese Patent Application Unexamined Publication No. 11-296251 (paragraphs 0009 to 0015, 0019, 0022, 0024 to 0029, and 0066 to 0068, and FIG. 2 and FIG. 3).
Patent literature 2: Japanese Patent Application Unexamined Publication No. 2002-325114 (paragraphs 0002, 0005, 0006, 0009 and 0010).
Usually, the modem operates in a quiet mode after the line is connected. A user does not recognize that communication is now being reset. The modem executes a reset to stably operate communication. The software modem is most unstable during the resetting of communication such as a resetting of a modulation system and a communication speed. The load on the CPU is largest during this resetting. If, while the CPU is being applied with large load, the CPU receives an interrupt request to process a specific application having a higher priority than that of a retraining processing and, for example, when there is an interrupt request to start a word processor or reproduce a DVD that applies large load on the CPU, the CPU usually executes the interrupt processing with priority over the retraining processing. Therefore, the retraining processing is not executed. When this processing continues for a long time based on the interrupt request, the CPU cannot communicate with the other communication apparatus to reset communication. Consequently, the retraining processing cannot be carried out normally, and the line is disconnected.
The information processor described in the patent literature 1 variably controls the clock frequency following the necessary load on the CPU that changes based on the negotiation state. On the other hand, the software modem described in the patent literature 2 changes the communication speed according to the number of applications being started, the state of the load of the applications being started on the CPU, and the time required for the modem processing. However, the above operations do not solve a problem of a line disconnection that occurs when the CPU executes the interrupt processing with priority over the retraining processing during the resetting of communication functions and performance which applies a large load to the CPU.